Abstract
The high-affinity receptor for immunoglobulin (Ig) E (Fc epsilon RI) on mast cells and basophils plays a key role in IgE-mediated allergies. Fc epsilon RI is composed of one alpha, one beta, and two gamma chains, which are all required for cell surface expression of Fc epsilon RI, but only the alpha chain is involved in the binding to IgE. Fc epsilon RI-IgE interaction is highly species specific, and rodent Fc epsilon RI does not bind human IgE. To obtain a "humanized" animal model that responds to human IgE in allergic reactions, transgenic mice expressing the human Fc epsilon RI alpha chain were generated. The human Fc epsilon RI alpha chain gene with a 1.3-kb promoter region as a transgene was found to be sufficient for mast cell-specific transcription. Cell surface expression of the human Fc epsilon RI alpha chain was indicated by the specific binding of human IgE to mast cells from transgenic mice in flow cytometric analyses. Expression of the transgenic Fc epsilon RI on bone marrow-derived mast cells was 4.7 x 10(4)/cell, and the human IgE-binding affinity was Kd = 6.4 nM in receptor-binding studies using 125I-IgE. The transgenic human Fc epsilon RI alpha chain was complexed with the mouse beta and gamma chains in immunoprecipitation studies. Cross-linking of the transgenic Fc epsilon RI with human IgE and antigens led to mast cell activation as indicated by enhanced tyrosine phosphorylation of the Fc epsilon RI beta and gamma chains and other cellular proteins. Mast cell degranulation in transgenic mice could be triggered by human IgE and antigens, as demonstrated by beta-hexosaminidase release in vitro and passive cutaneous anaphylaxis in vivo. The results demonstrate that the human Fc epsilon RI alpha chain alone not only confers the specificity in human IgE binding, but also can reconstitute a functional receptor by coupling with the mouse beta and gamma chains to trigger mast cell activation and degranulation in a whole animal system. These transgenic mice "humanized" in IgE-mediated allergies may be valuable for development of therapeutic agents that target the binding of IgE to its receptor.
Highlights
Cross-linking of the transgenic FceRI with human IgE and antigens led to mast cell activation as indicated by enhanced tyrosine phosphorylation of the FceRI [3 and ~/chains and other cellular proteins
Mast cell degranulation in transgenic mice could be triggered by human lgE and antigens, as demonstrated by [3-hexosaminidase release in vitro and passive cutaneous anaphylaxis in vivo
The results demonstrate that the human FceRI ix chain alone confers the specificity in human IgE binding, and can reconstitute a functional receptor by coupling with the mouse [3 and y chains to trigger mast cell activation and degranulation in a whole animal system
Summary
Generation of TransgenicMice Expressing the Human High-Affinity IgE Receptoroe Chain. The human genomic clone for the FceRI c~ chain that we reported previously [16] was used to construct the transgene. An 11.4-kb human genomic DNA fragment in the clone covering the entire structural gene plus a 1.3-kb promoter region and a 4.2-kb 3' flanking region was injected into mouse embryos to generate transgenic mice. The transgene in mice was confirmed by DNA hybridization. Mouse tail DNA was digested with EcoRI and hybridized to the previously reported human Fc~RI a chain cDNA [16]. Transgenic founders identified by hybridization were bred with C57BL/6J mice to obtain transgenic offspring for phenotypic and functional studies
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